The invention relates to stable adhesive compositions based on compounds containing ethylenic double bonds, which also contain organoboron compounds as initiators and which harden under the action of oxygen. Described here are particularly single-component cold-hardening reaction adhesives which are preferably based on methacrylic acid derivatives.
Adhesives which harden by polymerization of compounds containing ethylenic double bonds have been known for a long time. They can be prepared from methacrylic acid esters or acrylic acid esters of various alcohols by the addition of peroxides or hydroperoxides, as initiators, and other auxiliary adjuvants. Besides these, adhesive agents and filling agents are known for use in dentistry and surgery which contain, in addition to acrylic acid esters or methacrylic acid esters and other reaction partners containing ethylenic double bonds, trialkylboron compounds, such as triethylboron, tri-n-butylboron, etc., as an essential component. Such trialkylboron compounds have the disadvantage, however, that they are readily flammable, so that the handling of these adhesives presents considerable difficulties. It has tried to eliminate this inconvenience by reacting the trialkylboron compounds with 0.3 to 0.9 mol of oxygen.
It has also been tried to react the trialkylboron compounds with amines to reduce the spontaneous ignition. Due to these measures, the ignition temperature is displaced into a range of 0.degree. to 70.degree. C., but there is still considerable uncertainty in the handling of these mixtures. In particular, they are not suitable for structural bonding.
The polymerization systems described so far which use organoboron compounds as reaction initiator, are so-called binary systems, that is, the olefin containing portion to be polymerized are mixed with the separately stored organoboron compound only when their polymerization immediately following is intended. This applies particularly to cold-hardening systems, that is, for reaction mixtures which are to be subjected to polymerization at room temperature or at best at moderately elevated temperatures. Examples of such reaction systems using organoboron compounds as starters or initiators are described in DOS No. 23 21 215, U.S. Pat. No. 4,167,616 and British Pat. No. 1,113,722.